1871. ] Proceedings of the Asiatic Society. 93 
necessary that some accurate quantitative method should be devised, 
in order that every telegraph office may ascertain whether the 
resistance of their earth is higher or lower than the maximum 
resistance allowed. The principal difficulty met with is that, if 
the resistance between two earths be measured successively with 
positive and negative currents, the same result is not obtained. 
Consequently the ordinary law for a Wheatstone’s Bridge, or 
Differential Galvanometer, would not hold true. This difficulty, 
however, has been overcome in this paper, and formule are devel- 
loped suitable for a Wheatstone’s Bridge, a Differential Galvanome- 
ter, or simply for a Galvanometer of which the law of the deflec- 
tions is known. 
The details of some experiments are also given, and a particular 
instance is mentioned in which a much better ‘‘ earth” was obtain- 
ed by burying the plate in the upper stratum of soil than by bury- 
ing it much deeper, on account of a bed of sandstone that existed 
at about fifteen feet below the surface. 
Mr. Ayrton’s paper will be printed in full in the natural history 
part of the Journal. 
The following paper was received : 
Notes on the Country of Braj, by F. 8. Growse, Esq., M. A., 
my O. 8, 
This paper will be published in the first number of the philolo- 
gical part of the Journal which will appear shortly. 
Liprary. 
The following additions have been made to the library since the 
meeting held in March last. 
Presentations. 
*,.* Names of Donors in Capitals. 
Monatsbericht der Kéniglich Preussischen Akademie der Wis- 
senschaften zu Berlin, December 1870 :—AxKapEMIE DER WISSEN- 
SCHAFTEN zu BERLIN. 
Selections from the Records of the Government of India, Home 
Department, No. LXXVII; Papers relating to the Nicobar Islands : 
—Govt. of India, Home Dept. 
